This invention relates to smoking articles, such as cigarettes and cigars, and more particularly to smoking articles having an improved wrapping system, which produces a significant reduction in visible sidestream smoke without impairing the characteristics which allow for smoker acceptance and manufacturing feasibility.
A burning cigarette produces combustion products which exist in two phases. A gaseous phase consists of gases, such as CO.sub.2, and a particulate phase consists of droplets of high molecular weight products of thermal degradation. The particulate phase is visible and makes up what is normally referred to as "cigarette smoke."
Further, the smoke can be divided into two components. One is the mainstream smoke, the smoke which passes lengthwise through the cigarette to the smoker. The other is sidestream smoke, the smoke emitted into the atmosphere by a cigarette during static burning between puffs. Sidestream smoke constitutes a potential source of annoyance to the smoker and others in the vicinity. The growing awareness of this problem can be seen readily in the widespread passage of laws restricting smoking in public places. Therefore, significant market potential exists for a cigarette which would substantially reduce the amount of sidestream smoke.
The real need, however, is not simply for a cigarette with reduced sidestream characteristics. To be successful in the marketplace, the cigarette must also be acceptable to the consumer and readily adaptable to mass production manufacturing. A reduced-sidestream cigarette must meet the following four criteria to be commercially acceptable:
1. First, the cigarette must reduce sidestream smoke to such a degree that smokers not only can perceive the reduction, but also perceive the reduction as a desirable product benefit. Market research has been conducted to determine the degree of reduction necessary for this result. As this research shows, a minimum reduction of 50% of the visible sidestream smoke is necessary to achieve consumer acceptance. At the other extreme, a reduction of over 80 to 90% is undesirable, because the smoker wants to be able to determine whether the cigarette is lit. Also, it is suspected that the particulate portion of sidestream smoke may contribute to the annoyance of the smoker and others. Therefore, a reduced-sidestream product also should reduce sidestream particulate levels. PA0 2. The cigarette must exhibit acceptable taste characteristics. Smokers will not accept a persistent off-taste in order to achieve a reduction in sidestream smoke. A feasible product must achieve taste parity with existing products. PA0 3. The cigarette must exhibit acceptable performance characteristics. Such characteristics include puff count, burn continuity, ashing characteristics, and mainstream smoke delivery (e.g., "tar", nicotine). The consumer must perceive that the reduced-sidestream cigarette behaves similarly to "normal" cigarettes. It must deliver approximately the same number of puffs per cigarette, it must stay lit between puffs, and the ash must be sufficiently firm to maintain integrity, yet not interfere with normal smoking. Furthermore, modern consumers demand reduced levels of "tar" and nicotine, and would reject a product which failed to achieve parity for these parameters with current cigarette brands. PA0 4. The cigarette must be readily adaptable to mass production manufacturing techniques. Only through high-speed production can a cigarette be introduced to a mass market. Therefore, a reduced-sidestream product must not present undue difficulties in manufacturing. Areas of concern include tobacco blend composition, wrapper configuration, and demands for increased set-up time on cigarette making machines.
Two general approaches may be taken to the sidestream smoke problem. One is to reduce the total amount of sidestream material generated. This could be accomplished by reducing the amount of tobacco consumed during the smolder period between puffs, or by reducing the amount of smoke generated during combustion. Owens disclosed a cigarette incorporating a tobacco substitute, such as shredded carbon filled paper, in U.S. Pat. No. 3,902,504. The failure of cigarette manufacturers to produce a tobacco substitute that is acceptable to smokers, however, has prevented development of this concept.
Another approach is to reduce the amount of visible sidestream material. Here, the total amount of material released into the atmosphere during static burning may not be affected, but the droplets which constitute the particulate phase are reduced and the resultant stream is rendered invisible. The resulting smoke is thought to be less irritating, and thus less objectionable to consumers. This approach has yielded several candidates for a practical reduced-sidestream cigarette.
Most proposals for reducing sidestream smoke have concentrated on modifying the cigarette wrapper. An early effort by Kahane proposed a double-wrapped cigarette, in which the inner wrapper is a low-temperature melting-point, heat-insulating plastic, with a conventional outer wrapper. This design was said to reduce the burning temperature of the cigarette and lengthen the low-temperature distillation zone, thus making it perform like a pipe or cigar, reducing alleged health hazards. Although not the object of the invention, reduced sidestream smoke was cited as a product advantage. Worry about possible toxicity of the plastic wrapper combustion products has prevented commercial exploitation of this idea. Lippman, in U.S. Pat. No. 3,586,005, proposed a wrapper coated with a metal, e.g., aluminum, iron, or tin. The coated wrapper forms an ash in a tubular, unbroken sheath around the burned and burning tobacco, restricting airflow to the area through the burning zone. Although Lippman sought merely to reduce the production of "tar" through improved combustion of the tobacco, this invention also probably would reduce sidestream smoke. Testing this product, however, reveals that the resulting ash is so solid that when a consumer attempts to dislodge it, the ash tends also to pull the burning coal with it, extinguishing the cigarette. See McCarty, U.S. Pat. No. 3,744,496. Thus, this product has been rejected for commercial exploitation.
A more promising candidate was proposed by McCarty, U.S. Pat. No. 3,744,496. This cigarette includes a double wrapper, the inner wrap being a special carbon-filled paper. This product does exhibit a reduction in sidestream smoke, but consumer testing revealed a persistent acrid taste when smoked. Also, the product presents manufacturing difficulties stemming from the carbon-filled paper. The paper has proved difficult to adapt to cigarette-making machines, and tends to produce a high level of carbon dust in the work atmosphere. Thus, this development has not received commercial acceptance.
A completely new type of wrapper was proposed by Hind, U.S. Pat. No. 4,129,134. This wrapper consists of a single-layer polysaccharide film, and reduction of sidestream smoke is cited as one result. The resulting product does not look like a "normal" cigarette, however, and consumer preference for a product similar to existing cigarettes seems to have precluded development of this idea.
A single wrapper consisting of a paper containing magnesium oxides was advanced by Cline, U.S. Pat. No. 4,231,377. Testing has shown that this product does reduce sidestream smoke, but at the cost of an off-taste to consumers. Also, the product exhibits "flyaway" ash, which consumers perceive as a detriment.
Thus, twenty years of effort have produced no result. The simple fact that no commercially acceptable reduced-sidestream cigarette exists testifies eloquently to the ultimate failure of the prior art.
The present invention finds unexpected and surprising results in two areas of cigarette design, the wrapper configuration and burn additives. It is thus instructive to determine what the prior art teaches in each of these fields.
Although some proposals for reduced-sidestream cigarettes incorporate a double wrapper, no teaching suggests a cause and effect relationship.
Kahane proposed two cigarette configurations in U.S. Pat. Nos. 3,633,589 and 3,395,714. The '589 patent suggested a composite wrapper in which the sheets consisted of vegetable fiber stocks. The inner wrap was to be impervious to air, (such as a glassine or tracing paper) with the outer wrapper a conventional, porous sheet. This wrapper allegedly enriched the mainstream smoke by restricting airflow through the burning zone. To accomplish this result, the inner wrapper burned very slowly, leaving unburnt inner wrap up to the edge of the burning zone. The outer wrapper functioned to maintain burn continuity, confer desired ashing qualities, and mask undesirable appearance caused by the translucent inner wrapper. Nowhere was reduced sidestream smoke mentioned. Also, this invention presents a problem, in that the impervious inner wrapper prevents all airflow to the tobacco rod, causing the cigarette to self-extinguish between puffs. The '714 patent, discussed above, did mention reduced sidestream, but the effect was attributed to reduced burning temperature and a lengthened low-temperature distillation zone behind the burning zone. Again, the conventional outer wrapper presumably was included for appearance and ashing qualities, as in the earlier patent.
In Owens, U.S. Pat. No. 3,902,304, discussed above, a double wrapper is disclosed, but this cigarette is formed of multiple sections, each containing differing amounts of carbonized filler material. Each section is individually wrapped, and the outer wrapper merely encloses and lends structural integrity to the final product.
The composite wrapper shown in McCarty, U.S. Pat. No. 3,744,496, discussed above, results again from the unconventional appearance of the inner wrapper. The carbon-filled paper used here has a gray color, probably objectionable to consumers. The patent discloses two advantages of the double wrapper: reduction of tobacco weight and normal cigarette appearance. Rather than teaching any effect from the double wrapper, the inventor speculates that the reduction in sidestream stems from increased burning temperature due to the carbon filler.
The magnesium oxide paper disclosed by Cline, U.S. Pat. No. 4,231,377, discussed above, may be used in a double wrap configuration, according to the disclosure. Again, the cited advantages of double wrapping are tobacco weight reduction and cigarette appearance. Reduction of sidestream is attributed solely to the special magnesium oxide paper.
The common thread running through prior art disclosures of double-wrapped cigarettes is that reduction of sidestream smoke requires paper modifications that negatively affect the burning characteristics or appearance of the wrapper. The prior art teaches that these problems can be solved by wrapping the modified paper with a conventional paper. Not one of the proposed solutions teaches that double wrapping itself affects sidestream smoke.
A second critical feature of the present invention is the effect of burn additives upon sidestream smoke. Here, the prior art is not simply silent on the subject, but rather it points an investigator away from the solution.
Burn additives (also called burn chemicals) are well-known in cigarette manufacture. Their use stems from the fact that tobacco and paper tend to burn unevenly, leaving a loose, black or "flyaway" ash. Chemicals are thus added to cigarette paper to maintain burn continuity, to promote even burning, and to produce a white, firm ash. Studies by Resnik, et al, and Jodl demonstrate that the most effective burn additives are alkali metal salts, primarily citrates, phosphates, nitrates, and acetates of sodium and potassium. See Resnik, et al, "Factors Affecting Static Burning Rate," 21 Tobacco Science 103 (1977); Jodl, "Effect of Burning Additives of Cigarette Paper on Burning Rate of Cigarettes," 5(1) Beitr. Tabakforsch. 22 (1969). These references disclose the specific effects of various salts, and teach their use in concentrations ranging from 0 to 3%. No mention is made of any possible effect upon sidestream smoke.
U.S. patents contain similar teaching. In an early reference, Lanfry, U.S. Pat. No. 2,091,598, regards the use of potassium nitrate for burn enhancement as well-known, and suggests substituting a hydrocarbon oil for it to alleviate alleged harmful combustion products and disagreeable taste. Similarly, Cogbill, in U.S. Pat. No. 3,908,671, proposed a thermo-plastic wrap to reduce nicotine delivery. To promote burning, he taught the addition of potassium nitrate in concentrations ranging from 1.5 to 2.8% by weight. He teaches that addition of over 2.8% potassium nitrate should not be used, because the cigarette would then burn too fast. Another non-conventional wrapper is shown in Hind, U.S. Pat. No. 4,129,134, discussed above. Here, the reduction of sidestream is caused by a "shrinking" of the wrapper at the char line. The film-forming ingredient is said to be combined with an alkaline earth metal, preferably magnesium carbonate or calcium carbonate, but no proportions as percentage of the overall film weight is taught. Further the disclosure lumps two separate chemical paper additives, the burn additives, such as the citrates, and "fillers", such as calcium carbonate, both of which have distinct functions in the cigarette paper.
Two patents disclose a role for burn additives in sidestream reduction, but they expressly teach that burn chemicals cannot act to reduce sidestream without other chemical additives. McCarty, U.S. Pat. No. 3,744,496, discussed above, discloses that burn chemicals such as alkali metal hydroxides, bicarbonates, and carbonates, among others, act "synergistically" with the carbon filler in the paper to reduce sidestream smoke. The use of conventional fillers, from the alkaline earth metal carbonate group, preferably calcium carbonate, also enhance the sidestream smoke reduction. The amount of burning chemical as a proportion of the paper basis weight was not disclosed; the paper was stated to have been treated with solutions of sodium carbonate ranging from 0.5% to 5% concentration, well within the parameters disclosed by other authority. A similar role for burning chemicals was disclosed by Cline, U.S. Pat. No. 4,231,377, discussed above. Here, the burning chemical was said to enhance the sidestream reduction effect of the magnesium oxide paper filler. According to the disclosure, "neither magnesium oxide nor the chemical adjuvant salts when used alone as a filler or coating in smoking article wrappers substantially reduce sidestream smoke." The disclosure focused upon the use of sodium and potassium citrates and carbonates as burning chemicals in amounts ranging from 0 to 3.65% by weight.
The prior art can be summarized in three statements. First, no one has produced a commercially acceptable cigarette which exhibits reduced sidestream smoke characteristics. Second, no teaching exists which suggests that a double-wrapped cigarette would be particularly successful in reducing sidestream smoke. Third, the prior art teaches that burn additives, such as the alkali metal nitrates and citrates, cannot, by themselves, effectively reduce sidestream smoke.